1. Technical Field
The present invention relates to a manufacturing method for a ferroelectric memory device having a ferroelectric capacitor.
2. Related Art
A ferroelectric memory device is generally provided with a ferroelectric capacitor having a ferroelectric film composed of metal oxides. In the process for manufacturing such a ferroelectric memory device, if the ferroelectric film, after having been formed, is exposed to a reductive atmosphere such as hydrogen (H2) or water (H2O), the ferroelectric film is reduced, such that the electrical characteristics of the ferroelectric material is changed, causing a deterioration of the ferroelectric capacitor characteristics. In order to prevent this hydrogen damage, usually, a dielectric film having a hydrogen barrier function (AlOx or the like) is deposited on the capacitor as a hydrogen barrier film, after the capacitor is formed. For example, Japanese Unexamined Patent Application, First Publication No. 2004-119978 may be an example of relevant art. According to a known method in which hydrogen barrier films are provided, two hydrogen barrier films are formed. For example, Japanese Unexamined Patent Application, First Publication No. 2005-183843 may be an example of relevant art.
In case of a ferroelectric memory device having capacitors in a stacked structure, the capacitors can be densely disposed, and a ferroelectric memory cell array can be composed. However, when the capacitors are densely placed, a gap-fill technique is required for filling gaps between the capacitors with dielectric films. If the capacitors are covered by a dielectric layer without completely filling of the gaps between the capacitors, unfilled portions remain as voids, residual gas may stay there, and the gas causes the deterioration of the ferroelectric material with the passage of time, whereby the device reliability is lowered.
When gaps between adjacent capacitors are large enough, the capacitors could be covered without voids by an ordinary film forming method, such as, for example, a CVD method, without any special gap-fill technique.
However, in recent years, there have been greater demands for further miniaturization and higher integration of ferroelectric memory devices, and there are also demands for higher density in the capacitor arrangement. For example, the gap between adjacent capacitors is required to be less than 0.5 μm. When the gap between adjacent capacitor becomes so narrow, it would be difficult to fill the gap with the ordinary film forming method described above.
Generally, in ordinary wiring processes of the semiconductor manufacturing, narrow gaps between Al wirings are filled with high-density plasma (HDP) SiO2 films or SOG (spin-on-glass) films which have excellent coverage abilities.
However, in the process for manufacturing ferroelectric memory devices, gaps between the capacitors need to be filled without deteriorating the characteristics of the ferroelectric capacitors as described above, and this requirement causes greater difficulty compared to the case of filling gaps between metal wirings. The characteristics of the capacitors are damaged by both the high density plasma and the chemical attach of the hydrogen or water generated during the HDP or SOG film formation. For this reason, dielectric film forming and gap-filling techniques without any damage to the capacitor are required.